Process for the internal welding of plastic tubes

ABSTRACT

The invention relates to a process for manufacturing plastic packaging in tubular form, which process comprises a wrapping step during which a laminate ( 11 ) is wrapped, an abutting step during which the edges ( 8, 9 ) of the laminate ( 11 ) are butted together and a fastening step during which said edges ( 8, 9 ) of the laminate ( 11 ) are welded together, characterized in that a bead ( 12 ) of plastic in the molten state is extruded and deposited on the internal face of the packaging so as to cover at least the weld zone ( 10 ) defined between the edges. The energy needed to produce the weld ( 10 ) comes from the plastic bead ( 12 ). 
     The invention also relates to packaging obtained from the aforementioned process and to a device for implementing said process.

This application is the U.S. national phase of International ApplicationNo. PCT/IB2007/053842, filed 21 Sep. 2007, which designated the U.S. andclaims priority to EP Application No. 06121466.4, filed 28 Sep. 2006,the entire contents of each of which are hereby incorporated byreference.

FIELD OF THE INVENTION

The invention relates to the field of tubular packaging, especiallyconsisting of a wrapped plastic laminate. More precisely, the inventionrelates to wrapped laminates, the edges of which do not overlap.

PRIOR ART

The welding of the edges of a laminate so as to obtain a tubular bodyusually takes place with an overlap. See for example German PatentApplication DE 2008085.

When it is desired to place the edges face to face, a gap is leftbetween them which is filled with a material, such as a strip ofplastic, the strip acting as a welding element. See for this purposeEuropean Patent Application EP 0 000 643.

However, there is a need to bring the edges into direct contact witheach other (butt welding), for technical and aesthetic reasons. Buttwelding provides better continuity and homogeneity of the materialconstituting the wall of the packaging. In particular, it avoids contactbetween the product placed inside the tube with a barrier layer placedinside the laminate. Moreover, the absence of a welding element on theexternal face reduces the visibility of the weld zone.

Moreover, whether the edges are placed end to end with or without a gapcontaining a welding element, there is also a need to be able to reduce,if not eliminate, the visibility of the weld from the outside of thetube.

The heating systems of the prior art are placed on the outside of thetube and their activation necessarily results in a pronounced and mattweld zone.

GENERAL DESCRIPTION OF THE INVENTION

The problem the present invention proposes to solve lies in the weaknessof a butt weld and the maintaining of an attractive weld, i.e. one whichis unnoticeable or almost unnoticeable when observed from the outside.

In the invention, the solution to the aforementioned problem consists inreinforcing such a weld by means of a bead of plastic.

The invention relates in the first place to a process for manufacturingplastic packaging in tubular form, which process comprises a wrappingstep during which a laminate is wrapped, an abutting step during whichthe edges of the laminate are butted together and a fastening stepduring which said edges of the laminate are fastened together,characterized in that a bead of plastic in the molten state is extrudedand deposited on the internal face of the packaging so as to cover atleast the zone defined between the edges. One feature of the inventionlies in the fact that the energy needed to produce the weld comes fromthe plastic bead.

According to a first variant of the process according to the invention,the bead is deposited prior to the abutting step.

According to a second variant, the bead is deposited during the abuttingstep.

According to a third variant, the bead is deposited after the abuttingstep.

The bead may be placed beneath or above the weld zone.

The invention also relates to tubular packaging obtained by the processas defined above, the packaging being characterized in that it comprisesan element for reinforcing the zone defined between the edges, whichconsists of an extruded bead of plastic in the molten state.

Finally, the invention relates to a device for implementing a process asdefined above. The device is characterized in that it includes a weldingrod designed to be surrounded by a laminate, characterized in that itincludes means for extruding and placing a bead of plastic in the moltenstate between the external surface of the welding rod and a laminateplaced around said rod.

In one embodiment of the invention, the device includes a preheatedconveyor belt placed on the welding rod so that said bead is placedbetween said belt and a laminate wrapped around said rod.

In another embodiment of the invention, the device includes an externaldrive belt and an adjustable bearing block that are placed so as toexert, in the direction of said rod, pressure on a laminate and a beadof plastic which would be placed between said drive belt and said rod.

Advantageously, a device may be used for preheating the edges, forexample by contact, having the effect of increasing the temperature ofthe two edges of the laminate, thus facilitating or improving thewelding conditions.

Alternatively, or in addition, another device is used which is providedwith a hot-air blower so as to maintain the ambient air around the beadat a temperature of several hundred ° C. and consequently to avoid adrop in temperature of the bead as it passes from the exit of theextrusion head to the point where the bead is shaped.

According to one variant of the invention, the edges of the laminate arecut obliquely, this having the effect of increasing the lateral contactarea of the laminate in the weld zone. Such a configuration also enablesthe quality and the strength of the weld to be influenced.

In another variant of the invention, a bead is extruded with a shapeother than a cylinder, for example in the shape of an upside down T,thereby facilitating the shaping of the bead during welding.

Another variant of the invention consists in using a bead of coextrudedplastic (coextruded with a barrier material at the centre of the bead)so as to also guarantee, in the zone defined between the edges of thelaminate, good barrier protection from the external environment of thetube.

The present invention has several advantages, in particular:

-   -   a complex high-frequency welding system is no longer necessary,        the energy needed to produce the weld comes from the bead of        plastic;    -   the external appearance of the tube is perfect, given that the        energy for producing the weld is applied from the inside. With        the systems of the prior art, the energy is applied from the        outside, the weld being matt and pronounced; and    -   substantial covering layer (bead) made of PE or PP (or other        materials) inside the tube along the join between the two edges        of the laminate, preventing any contact between the product in        the tube and the barrier layer (e.g. aluminum) of the laminate.

DETAILED DESCRIPTION OF THE INVENTION

The invention will be described in greater detail below by means ofexamples illustrated by the following figures:

FIG. 1 is a perspective view of a first device according to theinvention;

FIG. 2 is a lateral section of the device of FIG. 1;

FIG. 3 is a perspective view of a second device according to theinvention;

FIG. 4 is a lateral section of the device of FIG. 3;

FIG. 5 is a perspective view of a third device according to theinvention;

FIG. 6 is a lateral section of the device of FIG. 5;

FIG. 7 is a perspective view of a fourth device according to theinvention;

FIG. 8 is a lateral section of the device of FIG. 7;

FIG. 9 is a perspective view of a fifth device according to theinvention;

FIG. 10 is a lateral section of the device of FIG. 9;

FIG. 11 shows a first variant of a weld according to the invention;

FIG. 12 shows a second variant of a weld according to the invention;

FIG. 13 shows a third variant of a weld according to the invention; and

FIG. 14 shows a fourth variant of a weld according to the invention.

LIST OF THE NUMERICAL REFERENCES USED IN THE FIGURES

-   1. welding rod-   2. Sizing die (height adjustable)-   3. Internal belt (metallic)-   4. Forming die-   5. Bearing block-   6. External belt-   7. Extrusion head-   8. First laminate edge-   9. Second laminate edge-   10. Weld zone-   11. Laminate (continuous strip)-   12. Bead of extruded plastic-   13. Barrier layer-   14. Gap-   15. Compression wheel-   16. Bead of coextruded plastic (coextruded with a barrier material    at the centre of the bead).

The tube is formed continuously by progressively wrapping a strip oflaminate 11 around the entire circumference of the welding rod 1, thelaminate being pulled (from left to right in the figures) through theforming die 4. The laminate 11 made of PE or PP (or other materials)(whether a monolayer or a multilayer) is then welded longitudinally bydepositing a bead 12 of extruded plastic in the molten state inside thetube.

Depending on the width of the laminate 11, it is possible to adjust thegap 14 between the edges 8, 9 of the laminate 11 formed on the finaldiameter of the tube. The bead 12 deposited inside may thus fill thisgap 14 (FIG. 12) and also weld the outer layer of the laminate 11, e.g.a multilayer laminate that contains a barrier layer 13. If necessary,the weld 12 may even partly cover an external portion of the edges 8, 9of the laminate 11 (FIG. 13). The use of a bead 12 of coextruded plasticin the molten state (coextruded with a barrier material 16 at the centreof the bead) also makes it possible to ensure that there is good barrierprotection in the gap 14 from the external environment of the tube (FIG.14). For aesthetic reasons, it is preferred to minimize this gap 14.

1st Variant:

FIGS. 1 and 2 illustrate the introduction of the bead 12, extruded inthe molten state, by means of a preheated conveyor belt 3 onto aheight-adjustable sizing die 2 after the cross section of the tube hasbeen definitively formed by the laminate 11 in a die 4. The weld bead 12is firstly applied against the inside of the preformed tube. The weld isthen sized to the desired dimensions (top welding).

2nd Variant:

FIGS. 3 and 4 show the engagement of a bead 12, extruded in the moltenstate, by means of a preheated conveyor belt 3 onto a height-adjustablesizing die 2 before the cross section of the tube has been definitivelyformed by the laminate 11 in the die 4. Thus, the edges 8, 9 of thelaminate 11, in its final shaping phase, are applied and pressed againstthe prepositioned bead 12 by means of an external drive belt 6 and anadjustable bearing block 5. The weld is therefore sized byprepositioning the bead 12, but in particular by the height adjustmentof the bearing block 5.

3rd Variant:

FIGS. 5 and 6 show a similar principle, but reversed, this time with thewelding from below. The bead 12, extruded in the molten state, isdeposited directly inside the tube after its circular cross section hasbeen definitively formed by the laminate 11 in the die 4. The weld isthen pressed and sized by means of the internal belt 3 and theheight-adjustable sizing die 2. In this variant, all the energy comingfrom the bead 12, needed to produce the weld, is transmitted directly tothe laminate 11, thus minimizing energy losses by contact, for example,with the internal belt 3.

4th Variant:

FIGS. 7 and 8 show the engagement of the bead 12, extruded in the moltenstate, but tensioned, avoiding the bead being deposited on the conveyorbelt 3. The energy losses are thus minimized as contact with theconveyor belt 3 is delayed as long as possible and takes place at thesame time as the operation of shaping and compressing the bead 12.

5th Variant:

FIGS. 9 and 10 show the engagement of the bead 12, extruded in themolten state, but tensioned, the bead 12 being directly driven by thelaminate 11 and no longer requiring a conveyor belt. The weld is thenpressed and sized by a compression wheel 15 or, alternatively, by acompression block 2 (not illustrated).

Of course, the invention is not limited to the aforementioned examples.

1. Process for manufacturing plastic packaging in tubular form, saidprocess comprising: a wrapping step during which a laminate, havingedges, is wrapped, an abutting step during which the edges of thelaminate are butted together, and a fastening step during which saidedges of the laminate are welded together, wherein a bead of plastic ina molten state is extruded and deposited on an internal face of thelaminate so as to cover at least a weld zone defined between the edges,the energy needed to produce the weld coming from the plastic bead, andwherein the bead of plastic is extruded in the molten state onto aconveyor belt, and the molten bead of plastic contacts the internal faceof the laminate prior to the abutting step.
 2. Process according toclaim 1, wherein the bead is placed in the molten state beneath saidweld zone.
 3. Process according to claim 1, wherein the bead consists ofa plastic coextruded with a barrier material at the centre of the bead.